Compositions of gas generates with polymer adhesive

ABSTRACT

Compositions of gas generants with polymer adhesive are disclosed. The gas generant compositions include nitrogen containing guanidines, hydrogen containing tetrazole, oxidizing agent, polymer adhesive, and residue aggregating agent. The nitrogen containing guanidines range from 25 to 45 weight percent. The hydrogen containing tetrazole is 10-30 weight percent. The nitrate oxidizing agent is 20-40 weight percent. The perchlorate oxidizing agent ranges from 1 to 15 weight percent. The polymer adhesive is 0.1-3 weight percent and the residue aggregating agent weights from 1 to 15 weight percent. The gas generant pellets are applied to inflators for generating gas so that the air bag is inflating instantly for protecting driver and passengers in automobile.

BACKGROUND OF THE INVENTION

The present invention relates to chemical compositions, especially to gas generants containing polymer adhesive that are applied to inflators for generating gas to inflate air bag.

In order to reduce the casualties in car accidents, the bag in air bag system is inflated quickly to protect the driver and the passengers when the sensor is sensing the crash of the car. In early days, sodium aizde gas generant is used most common for generating gas to inflate the air bag. The advantages of sodium aizde gas generants are producing non-toxic gases and generating low flame temperature gas. The costs of raw materials are low. The sodium azide gas generants have long storage stability and good safety property. However, sodium aizde is a toxic compound that leads to uncomfortable feelings such as headaches and rapid breathing when people are breathing the sodium azide powder.

Moreover, sodium aizde is easy to react with heavy metal to form highly-reactive and unstable compounds. Thus some special safety methods are required for handling the raw materials and the process for the gas generants. When vehicles are going to be scrapped and airbags are not used yet, the toxic sodium aizde in the unused air bags needs to take special treatment.

Now manufactures of air bag inflators in US or Europe are dedicated to develop alternatives for sodium aizde. The common points for sodium aizde alternatives are adopting organic compounds with high nitrogen content as fuels. After reacting with oxidizing agents, the non-toxic gas is generated to inflate the air bag connected with the inflator.

Refer to U.S. Pat. No. 5,460,668—Nonazide gas generating compositions with reduced toxicity upon combustion disclosed by Lyon, Lyman R. The gas generant containing organic compound fuel with high nitrogen content includes 5-aminotetrazole and its potassium salt serving as fuel, strontium nitrate using as oxidizer, glass powder using as heat absorbing additive for reducing the combustion temperature. However, the glass powder needs the property of high glass transition temperature. When the reacting temperature of the gas generant is higher than the glass transition temperature, the glass powder will melt into liquid form and flow freely through filter of the inflator so that the glass powder will not sediment on the filter. Furthermore, it will reduce the filtering effect in the inflator.

Refer to U.S. Pat. No. 6,547,900—Method of stabilizing the density of gas generant pellets containing nitroguanidine disclosed by Canterberry, J. B. Nitroguanidine is used as fuel. The phase stabilized ammonium nitrate is used as oxidizer. The nitroguanidine is ground to powder for increasing the mechanical strength of pellets. The amount of residues is less during the combustion of gas generant. It will produce tolerable levels of toxic gases. However, the phase stabilized ammonium nitrate is easy to degrade due to moisture. The degradation will make the gas generant losing the stability.

Refer to U.S. Pat. No. 6,123,359—Inflator for use with gas generant compositions containing guanidines disclosed by Cabrera, Raul etc., another gas generant is revealed. The fuels are selected from the group consisting of guanidine nitrate, nitroguanidine, triaminoguanidine nitrate, diaminoguanidine nitrate and monoguanidine nitrate. The ammonium perchlorate is used as oxidizer. However, the ammonium perchlorate will generate a lot of hydrogen chloride gas after reaction. Thus iron oxide and copper chromite or mixtures thereof are added as catalysts for overcoming problem of HCl generating by the combustion of ammonium perchlorate.

Thus there is a need to develop a new gas generant containing polymer adhesive to improve above disadvantages.

SUMMARY OF THE INVENTION

Therefore it is a primary object of the present invention to provide a gas generant containing polymer adhesive that generates gas quickly for inflating air bags within milliseconds. Moreover, it produces tolerable levels of toxic gases.

It is another object of the present invention to provide a gas generant containing polymer adhesive that enables the compositions of gas generant forming pellets with better radial tensile strength and axial tensile strength. Moreover, it can enhance the quality of pellets and the reproducibility of the performance.

It is a further object of the present invention to provide a gas generant containing polymer adhesive that uses aggregating agent to make the solid residue from combustion of the gas generant aggregating into clot whose diameter is larger than that of the screen of the filter. Thus it can reduce both the load of the filter and the amount of the filter used. Furthermore, the cost of the filter is decreased.

It is a further object of the present invention to provide a gas generant containing polymer adhesive that is made in the form of pellets. It is applied to the air bag systems of the car under the temperature range from −35° C. to 85° C. The air bag is inflated within milliseconds so as to protect the driver and passengers in time.

A gas generant with polymer adhesive according to the present invention contains 25-45 weight percent nitrogen containing guanidines, 10-30 weight percent hydrogen containing tetrazole or its salts, 20-40 weight percent nitrate oxidizing agent, 1-15 weight percent perchlorate oxidizing agent, 0.1-3 weight percent polymer adhesive, and 1-15 weight percent residue aggregating agent. The nitrogen containing guanidines are mixed with the hydrogen containing tetrazole or its salts as fuel. After the nitrogen containing guanidine reacting with the oxidizing agent, the concentration of generated gas is tolerable. The hydrogen containing tetrazole or its salts can reduce the flame temperature and increase the amount of gas generated. The nitrate oxidizing agent as well as the perchlorate oxidizing agent can increase the reaction rate of gas generant. The polymer adhesive can improve the radial tensile strength and axial tensile strength of pellets of the gas generant. In addition, the residue aggregating agent is used for aggregating the reaction product of alkaline metal oxide so as to improve the efficiency of the filter.

BRIEF DESCRIPTION OF THE DRAWING

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawing, wherein

The FIGURE is a pressure-time curve of an embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A gas generant with polymer adhesive according to the present invention includes fuel, oxidizing agent, polymer adhesive, and residue aggregating agent. The fuel consists of nitrogen containing guanidines compound, hydrogen containing tetrazole or its salts. The oxidizing agents include nitrate oxidizing agent and perchlorate oxidizing agent. The present invention contains 25-45 weight percent nitrogen containing guanidines, 10-30 weight percent hydrogen containing tetrazole or its salts, 20-40 weight percent nitrate oxidizing agent, 1-15 weight percent perchlorate oxidizing agent, 0.1-3 weight percent polymer adhesive, and 1-15 weight percent residue aggregating agent.

The nitrogen containing guanidine is selected from one of the followings: guanidine nitrate, monoaminoguanidine nitrate, triaminoguanidine nitrate, or nitroguanidine. Nitroguanidine is a white crystalline solid, non-hygroscopic and easily soluble in alkali solution. The diameter of particle ranges from 3 to 10 μm and the density is 1.715 g/cm³. It melts at 232° C., deflagrates at 275° C. and generates gases containing carbon dioxide, nitrogen gas and water vapor after reacting with oxidizing agents. The concentrations of harmful gases such as carbon monoxide (CO) or nitrogen oxides (NOx) generating wherefrom are tolerable, no harm to human health. Thus nitroguanidine is preferable and the preferred amount is 30-40 weight percent.

The hydrogen containing tetrazole or its salts is selected from one of the followings: 5-nitrotetrazole, 5-aminotetrazole, or potassium salts of 5-aminotetrazole. The 5-aminotetrazole is white powder with density of 1.653 g/cm³. It can reduce the flame temperature and increase the gas amount while the chemical reaction happening. When being applied to the inflators in air bag, it can effectively reduce the temperature in combustion chamber and its outlet. Thus the 5-aminotetrazole is preferable and the preferred amount is 15-25 weight percent.

Oxidizing agents are the main source of oxygen when combustion reactions take place. Thus the amount of oxidizing agents used depends on the oxygen required by the stoichiometric combustion reaction. During the combustion reaction, most carbon monoxide will be oxidized into carbon dioxide by the oxygen provided from oxidizing agents. The oxidizing agents include nitrate oxidizing agent and perchlorate oxidizing agent. The nitrate oxidizing agent is alkaline metal nitrate or alkaline earth metal nitrate while the perchlorate oxidizing agent is alkaline metal perchlorate or ammonium perchlorate. The diameter of the alkaline metal nitrate or alkaline earth metal nitrate particle ranges from 10 to 30 μm. The alkaline metal nitrate or alkaline earth metal nitrate is selected from a group of lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, or strontium nitrate while potassium nitrate is preferable with the amount from 25 to 35 weight percent.

The oxygen content of the alkaline metal perchlorate or ammonium perchlorate is higher than that of the alkaline metal nitrate or alkaline earth metal nitrate. The gas generant with perchlorate salts according to the present invention is easy to ignite and the combustion efficiency of the gas generant is improved. Thus the gas generant produces gas quickly to inflate the air bag. The diameter of the alkaline metal perchlorate or ammonium perchlorate particle ranges from 5 to 20 μm. The alkaline metal perchlorate or ammonium perchlorate is selected from lithium perchlorate, sodium perchlorate, potassium perchlorate, or ammonium perchlorate while potassium perchlorate is preferable with the amount from 5 to 10 weight percent.

The polymer adhesive is selected from cellulose derivatives, starch, and vinyl alcohol acetate resin while vinyl alcohol acetate resin is preferable with the amount from 0.5 to 1.5 weight percent. It makes the pelletizing machine pressing pellets of the present invention with different shapes easily. The products have higher radial tensile strength and axial tensile strength mechanical properties. Thus pellets of the present invention will not break easily during packaging and transportation processes. Moreover, the stable initial burning surface area of the pellets can enhance the combustion performance of the air bag inflator.

The residue aggregating agent is used for aggregating alkaline earth metal oxide or alkaline metal oxide generating from the oxidizing agent during the combustion reaction. The filter of the air bag inflator can easily filter the aggregates of alkaline earth metal oxide or alkaline metal oxide to increase the efficiency of the filter. The residue aggregating agent is selected from clay, talc powder, and silicon dioxide. The diameter of the residue aggregating agent particle ranges from 7 to 20 nm. The surface area of silicon dioxide ranges from 100 to 300 m² per gram is measured by Brunauer-Emmett-Teller (BET) method. The silicon dioxide is preferable and the amount ranges from 4 to 10 weight percent.

In summary, the gas generant according to the present invention provides lower combustion temperature and anti-aging function. By the polymer adhesive, the pellets of gas generant have better mechanical properties. It can improve the manufacturing, packaging and transportation processes. The combustion efficiency is also improved. Thus the air bag inflator with the present invention has lower flame temperature and higher combustion efficiency. It can inflate the bag in time to protect the driver and passengers during car accidents.

Gas generant compositions are formulated according to the table 1 below (amounts in parts by weight). It shows a comparison between vinyl alcohol acetate resin and starch. The combustion temperature, carbon monoxide concentration and carbon dioxide concentration are calculated by computer program CEC 76 of NASA (National Aeronautic and Space Administration) at the pressure of 1000 psi.

TABLE 1 component Example 1 Example 2 nitroguanidine 35%  35%  5-aminotetrazole 19%  19%  potassium nitrate 30.5%   30.5%   potassium 7.5%   7.5%   perchlorate silicon dioxide 7% 7% (SiO₂) vinyl alcohol 1% 0% acetate resin (VAAR) starch 0% 1% combustion 1998 K 2311 K temperature carbon monoxide 6.94E−2 7.33E−2 concentration carbon dioxide 7.52E−2 7.72E−2 concentration

As shown in table 1, combustion temperature is the temperature inside the air bag inflator after combustion of the gas generant. The vinyl alcohol acetate resin used by the present invention has lower combustion temperature than starch used in conventional gas generant. Therefore, it can reduce the cooling load of the filter in air bag inflator. Moreover, the gases generating by the combustion of gas gererant with vinyl alcohol acetate resin have lower carbon monoxide concentration and carbon dioxide concentration. The gas generant of the present invention can be stored in the form of pellets. The vinyl alcohol acetate resin makes the pellets having higher radial tensile strength and axial tensile strength so that the damage of pellets during packaging and transportation is reduced. Furthermore, the stable initial burning surface area of the pellets makes the air bag inflator have more stable pressure during the combustion reaction.

Example 1

The gas generant composition is prepared by taking 10 gm vinyl alcohol acetate resin in a stirring machine, dissolving it into 1000 ml industrial alcohol, adding 70 gm silicon dioxide with average diameter of 10 nm, 350 gm nitroguanidine with average diameter of 5 μm, 190 gm 5-aminotetrazole with average diameter of 10 μm, 305 gm potassium nitrate with average diameter of 20 μm, and 75 gm potassium perchlorate with average diameter of 10 μm in order, stirring the mixture into p aste, heating the paste at 60° C., stirring continuously until the industrial alcohol evaporates, using a screen with screen sizing of 425 μm to crush the product, heating the mixture in an oven setting at 105° C. for 24 hours, then the dried mixture is cooled down to room temperature. The dried mixture is pressed into pellets with 6 cm diameter×4 cm height by a pelletizing machine. The radial tensile strength of the pellet is 16 kg/cm² and the axial tensile strength of the pellet is 15 kg/cm².

The gas generant composition of the present invention is pressed into strands with size of 5×5×40 cm³ by using a mold in oil press machine setting at 20 tones pressure for 40 seconds. Then the surfaces of the strand are covered with epoxy resin containing 20% TiO₂ to improve the end-burning effect. The measurements of the burning rate of the gas generant strands are carried out with a strand burner made by Atlantic Research Corporation. The strand burner is installed in temperature chamber operated under 30 kg/cm² of nitrogen pressure at 20° C. The strand is ignited by a 0.7 mm diameter nickel-chrome wire heated electrically. The lead lines are used to measure the combustion time of the strand. The burning rate is 9.18 cm per second according to the combustion distance and the combustion time of the strand. After combustion, the solid residue aggregates into porous material with good sintering property.

The drop hammer test result of the gas generant according to the present invention is 7.5 joule. When the gas generant obtains energy larger than 7.5 joule, a reaction will occur. Moreover, a friction sensitivity test is carried out and the result is larger than 360 Newton force. The auto ignition temperature of the present invention is 230° C. so that once the gas generant compositions of the present invention is placed in an environment at 230° C., spontaneous combustion will occur. After combustion, each gram of the gas generant generates 802 calorific capacities. The gas generant liberates 0.0586 ml gas per gram while being tested by the vacuum stability test at 100C. Therefore, the gas generant according to the present invention has good thermal stability and vacuum stability.

Example 2

The manufacturing processes of this example are the same with above one while the VAAR is replaced by starch. The combustion temperature, carbon monoxide concentration and carbon dioxide concentration of this example are all higher than those of the example one.

Example 3-5

Gas generant compositions are formulated according to table 2 below (amounts in parts by weight). As shown in table 2, the amounts of potassium nitrate and potassium perchlorate are different in different examples.

TABLE 2 component Example 3 Example 4 Example 5 nitroguanidine 33% 33% 33% 5-aminotetrazole 23% 23% 23% potassium nitrate 35% 30% 25% potassium  0%  5% 10% perchlorate silicon dioxide 8.6%  8.6%  8.6%  (SiO₂) vinyl alcohol 0.4%  0.4%  0.4%  acetate resin (VAAR) combustion 1910 K 1929 K 2001 K temperature carbon monoxide 7.49E−2 7.70E−2 7.95E−2 concentration carbon dioxide 5.72E−2 6.27E−2 6.78E−2 concentration

The combustion temperature, carbon monoxide concentration and carbon dioxide concentration are calculated by the computer program CEC76 of NASA (National Aeronautics and Space Administration).

The manufacturing processes of these examples are the same with the example one. The potassium perchlorate contains more oxygen than the potassium nitrate so that the gas generant with more potassium perchlorate will burn more easily and generates gas to inflate the airbag more quickly.

Example 6-8

Take 27 gm pellets of the example 1 and put them into the driver side inflator. Respectively put the inflator at a temperature chamber at −35° C., 22° C. and 85° C. for two hours. Take the inflator out of the temperature chamber and place it in a 60-liter ballistic tank within three minutes. Use pyrotechnic squib and 0.7 gm potassium nitrate—boron to ignite the gas generant pellets in inflator. The pressure towards time curve of the 60-liter ballistic tank, as shown in the FIGURE, is recorded with 20 KHz sampling frequency by using Nicolet data acquisition system of the US company. Table 3 shows the experimental data of the inflators under different environmental temperatures.

TABLE 3 Example 6 Example 7 Example 8 environmental −35 ± 3 22 ± 3 85 ± 3 temperature(° C.) Pellets filled in 27 27 27 the inflator (g) inflator weight 404.06 404.18 404.39 before combustion(g) inflator weight 381.69 381.57 381.65 after combustion (g) (g) weight loss (g) 22.37 22.61 22.74 residue weight in 0.69 0.70 0.72 the 60-liter ballistic tank (g) maximum 1.96 2.13 2.14 pressure in the 60-liter ballistic tank (bar) time arriving the 60 56 53 maximum pressure (millisecond)

As shown in table 3, the gas generant pellets of the present invention are respectively filled into the air bag inflator at three different temperature conditions—35° C., room temperature and 85° C. After igniting the gas generant pellets will achieve maximum pressure and inflate the air bag for protecting the drivers and passengers in the car. Refer to the FIGURE, a pressure vs. time curve in the 60 liter ballistic tank at three different temperature conditions is disclosed.

The first, the second and the third curves respectively represent pressure change over time in the air bag inflator at 85° C., 22° C., and −35° C. In the 53 millisecond, the first curve achieves maximum pressure 2.14 bar while the second curve achieves maximum pressure 2.13 bar after 56 millisecond and the third curve achieves maximum pressure 1.96 bar after 60 millisecond.

The above three curves are generated by testing the gas generant of the present invention under extreme environment conditions for human being. The gas generant according to the present invention can achieve maximum pressure within 30-60 milliseconds in the habitable temperature range and inflate the air bag quickly for protecting the driver and passengers. Thus the air bag can provide protection in time.

Back to the table 3, 27 g pellets of the gas generant are used under three different temperatures. After combustion, average weight loss of the air bag inflator is 22.57 g. The average weight of the residue on the wall of the 60-liter ballistic tank generated from the air bag inflator is 0.70 g. Therefore, the average weight of the pellets of the gas generant changing from solid to gas is 21.87 g. Thus in average, 81 weight percent of the solid pellet is converted into gas for providing better combustion efficiency and inflating the air bag more quickly.

Within the 60-liter ballistic tank, gas generated by the gas generant pellet according to the present invention is collected and measured the concentration. The gas includes carbon monoxide and carbon dioxide while carbon monoxide concentration is 23152 ppm (Part Per Million) and carbon dioxide concentration is 26714 ppm. When the air bag inflator is applied to a car with volume of 2.7 m³, the gas concentration is diluted into one to forty-fifth. Thus the carbon monoxide concentration becomes 514 ppm and carbon dioxide concentration becomes 594 ppm. According to Documentation for Immediately Dangerous to Life or Health Concentrations of NIOSH (National Institute for Occupational Safety and Health), tolerable concentration of carbon monoxide is 1500 ppm and that of carbon dioxide is 50000 ppm. Thus concentration of gas generated by the present invention falls within the tolerable concentration range disclosed in the above documentation and is not harmful to human heath.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 

1. Gas generant compositions comprising: 25-45 weight percent nitrogen containing guanidines; 10-30 weight percent hydrogen containing tetrazole or salts thereof; 20-40 weight percent nitrate oxidizing agent; 1-15 weight percent perchlorate oxidizing agent; 0.1-3 weight percent polymer adhesive; and 1-15 weight percent residue aggregating agent.
 2. The gas generant compositions as claimed in claim 1, wherein the nitrogen containing guanidine is selected from the group consisting of guanidine nitrate, monoaminoguanidine nitrate, triaminoguanidine nitrate, and nitroguanidine group.
 3. The gas generant compositions as claimed in claim 1, wherein the hydrogen containing tetrazole or salts thereof is selected from the group consisting of 5-nitrotetrazole, 5-aminotetrazole, and potassium salts of 5-aminotetrazole.
 4. The gas generant compositions as claimed in claim 1, wherein the nitrate oxidizing agent is alkaline metal nitrate or alkaline earth metal nitrate.
 5. The gas generant compositions as claimed in claim 4, wherein the alkaline metal nitrate or alkaline earth metal nitrate is selected from the group consisting of lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, and strontium nitrate.
 6. The gas generant compositions as claimed in claim 1, wherein the perchlorate oxidizing agent is alkaline metal perchlorate or ammonium perchlorate.
 7. The gas generant compositions as claimed in claim 6, wherein the alkaline metal perchlorate or ammonium perchlorate is selected from the group consisting of lithium perchlorate, sodium perchlorate, potassium perchlorate, and ammonium perchlorate.
 8. The gas generant compositions as claimed in claim 1, wherein the polymer adhesive is selected from the group consisting of cellulose derivatives, starch and vinyl alcohol acetate resin.
 9. The gas generant compositions as claimed in claim 1, wherein the residue aggregation agent is silicon dioxide.
 10. The gas generant compositions as claimed in claim 1, wherein particle diameter of the nitrogen containing guanidines ranges from 3 to 10 μm.
 11. The gas generant compositions as claimed in claim 1, wherein particle diameter of the hydrogen containing tetrazole or salts thereof ranges from 5 to 20 μm.
 12. The gas generant compositions as claimed in claim 1, wherein particle diameter of the nitrate oxidizing agent ranges from 10 to 30 μm.
 13. The gas generant compositions as claimed in claim 1, wherein particle diameter of the perchlorate oxidizing agent ranges from 5 to 20 μm.
 14. The gas generant compositions as claimed in claim 1, wherein particle diameter of the residue aggregating agent ranges from 7 to 20 nm. 